1. Field of the Invention
The present invention relates to an anti-jackknife system and, particularly, to a system for preventing a jackknife condition while allowing normal backing of a tractor-trailer rig and without interferring with normal steering of such a rig.
2. Description of the Prior Art
Tractor-trailer rigs are very well-known to highway travelers. Typically, such rigs are formed of two primary units--a trailer which is towed by a tractor, the trailer being connected to the tractor by a fifth-wheel assembly. The primary elements of the fifth-wheel assembly include a wheel plate carried by the tractor and a fifth-wheel pin. The pin and wheel plate provide a pivotal connection between the trailer and tractor.
A "jackknife" condition is a concern to all tractor-trailer rig drivers, whether they have experienced such a condition or not. The term "jackknife" is commonly employed to describe a misalignment between the trailer and tractor with the trailer pivoting, out of control, about its fifth-wheel pivot connection to the tractor.
Several devices have been proposed for controlling a jackknife condition. For example, Capps U.S. Pat. No. 4,119,330 provides abutments on opposing sides of the fifth-wheel plate with a stop being provided on the trailer. In the event of a jackknife condition, the stop will engage one of the abutments to limit the extent of the jackknife condition. However, so as to not unduly interfere with normal operation of the tractor-trailer rig, the stop/abutment system of Capps is operative only after the jackknife condition has advanced to a significant degree. Capps also discloses an electromagnetic system to restrain pivotal movement between the tractor and trailer.
Kornoelje U.S. Pat. No. 3,963,265 describes a system in which a vertically retractable pin is employed to engage stops located on the underside of the trailer. The pin is biased to an extended or elevated (stop engaging) position and retracted by a fluid system to permit normal turning of the tractor-trailer rig. Other systems are disclosed in U.S. Pat. Nos.: 3,883,160; 3,733,090; 3,701,547; 3,618,983; and 4,341,395.